With the booming of the Wimax (World Interoperability for Microwave Access), the third generation mobile communication system has to improve its network performance and reduce costs of the network construction and operation to maintain its powerful competence in the mobile communications field. Therefore, the standardization workgroup of the 3GPP (the 3rd Generation Partnership Project) is now focusing on the research of evolution of the PS Core (Packet Switch Core) and the UTRAN (Universal Mobile Telecommunication System Radio Access Network). The research project is called System Architecture Evolution (SAE) aiming at higher transmission rate, shorter transmission time delay, optimized packet and support of mobility management among the E-UTRAN (Evolved UTRAN), UTRAN, WLAN (Wireless Local Area) and other non-3GPP access networks provided by the Evolved Packet Core (EPC).
As shown in FIG. 1, at present the architecture of the SAE comprises the following network elements:
an E-RAN (Evolved RAN): an Evolved Radio Access Network, providing higher uplink and downlink rate, lower transmission delay and more reliable wireless transmission. The network element included in the E-RAN is eNodeB (Evolved NodeB, evolved base station) to provide wireless resources for user access.
a PDN (Packet Data Network): a network for providing services to users.
an E-Packet Core: an evolved packet network, providing lower delay and allowing accesses of more wireless access systems, comprising the following network elements:
an MME (Mobility Management Entity): a control plane function entity, a server for temporarily storing user data, being responsible for managing and storing the context of a UE (such as identification of the UE/User, mobility management state, and user security parameter etc.), allocating temporary identifications to users, when the UE is located in this tracking area or this network, performing authentication to this user, processing all non-access layer messages between the MME and the UE, and triggering paging in the SAE. The MME is a mobility management unit in the SAE system, while the mobility management unit is the SGSN (Serving GPRS Support Node) in the UMTS (Universal Mobile Telecommunications system).
a Serving GW (Gateway): this gateway is a user plane entity, being responsible for processing the user plane data routing and terminating the downlink data of the UE in an idle (ECM_IDLE) state, managing and storing the SAE bearer context of the UE, such as an IP bearer service parameter and a network internal routing information etc. The Serving GW is an anchor point of the internal user plane in the 3GPP system and there is only one Serving GW for one user at one time.
a PDN GW: a Packet Data Network Gateway, a gateway being responsible for enable the UE to access the PDN, allocating IP addresses for users, and meanwhile being the mobility anchor point of the access systems of the 3GPP and the non-3GPP. The functions of the PDN GW further comprise: policy implementation, charging support and so on. A user may access a plurality of PDN GWs simultaneously. A PCEF (Policy and Charging Enforcement Function) is located in the PDN GW as well.
a PCRF (Policy and Charging Rules Function): responsible for providing policy control and charging rules to the PCEF.
an HSS (Home Subscriber Server): for permanently storing user subscription data. The contents stored in the HSS comprise an IMSI (International Mobile Subscriber Identification) of the UE and the IP address of the PDN GW.
Physically, the Serving GW and the PDN GW may be combined as one. The user plane network elements of the EPC system comprise the Serving GW and the PDN GW.
When the UE (User Equipment) moves in the EPC, a mobility management may occur for the UE: when the UE moves to a new tracking area list, a TAU (Tracking Area Update) process may occur between the UE and the network; when the UE is in an ECM_CONNECTED state, the UE moves to a new eNodeB, an HO (Handover) process will occur for the UE. When the TAU or the HO process occurs for the UE, the Serving GW connected to the UE may change, and thus the Serving GW needs to send a bearer update request message to the PDN GW to update the bearer between the Serving GW and the PDN GW.
During the TAU or the HO process where the Serving GW changes in the prior art, there are two manners of updating the bearer between the Serving GW and the PDN GW: one manner is, upon receiving a bearer establishing request message from the mobility management unit (the MME or the SGSN), the Serving GW immediately sends a bearer update request message to the PDN GW to update the bearer between the Serving GW and the PDN GW (as shown in FIG. 2); the other manner is the Serving GW sends the bearer update request message to the PDN GW to update the bearer between the Serving GW and the PDN GW only after it acquires the address of the eNodeB and a TEID (Tunnel Endpoint Identifier) (as shown in FIG. 3). Since there are two manners of updating the bearer between the Serving GW and the PDN GW by the Serving GW, if the mobility management unit does not indicate the Serving GW when to update the bearer between the Serving GW and the PDN GW, it may possibly occur that the Serving GW updates the bearer between the Serving GW and the PDN GW too early or too late.